The present invention relates to a down-the-hole drill (“DHD”) hammer. In particular, the present invention relates to a DHD hammer having a reverse exhaust system and a segmented chuck assembly.
Typical DHD hammers include a piston that is moved cyclically with high pressure gas (e.g., air). The piston generally has two end surfaces that are exposed to working air volumes i.e., a return volume and a drive volume that are filled and exhausted with each cycle of the piston. The return volume pushes the piston away from its impact point on a bit end of the hammer. The drive volume accelerates the piston toward the impact point.
Typical DHD hammers also combine the exhausting air from the working air volumes into one central exhaust gallery that delivers all the exhausting air through the drill bit and around the externals of the DHD hammer. In most cases, about 30% of the air volume is from the DHD hammer's return chamber, while about 70% is from the hammer's drive chamber. However, this causes much more air then is needed to clean the bit-end of the hammer (e.g., the holes across the bit face). Such high volume air passes through relatively small spaces creating high velocity flows as well as backpressure within the DHD hammer. This is problematic as such high velocity air along with solids (e.g., drill cuttings) and liquids moved by the high velocity air causes external parts of the DHD hammer to wear more rapidly while backpressures within the DHD hammer reduces the tool's overall power and performance.
Further, when DHD hammers are used, the DHD hammer is typically immersed in water that includes drill cuttings and debris. Such water and debris can have adverse effects upon a DHD hammer's operation and performance if allowed to enter the internal areas of the DHD hammer. Notwithstanding, conventional DHD hammers typically include a piston with a thru-hole that allows for working air volumes from the drive chamber to be exhausted through the piston and out through the drill bit. As such, an open flow path exists for fluids to exit the DHD hammer's drive chamber through the drill bit. This in turn provides an open flow path for fluids to enter the drive chamber when working fluid volumes are not being exhausted from the DHD hammer, such as when the DHD hammer is not being used, yet is still immersed in the drill hole. This frequently occurs when drill pipes are added to a drill sting to advance a bore hole.
Typical DHD hammers also include a chuck assembly having an integrally formed chuck i.e., a chuck formed as a single part. Such typical chucks, which are threadedly connected to the DHD hammer casing operate to engage shank splines of a drill bit to provide for rotational movement. This movement of the drill bit within the chuck however, results in increased shank stresses created by the relatively small torque transmission diameter of the shank compared to the head of the drill bit and because of the high intensity elastic strain wave that passes through the small diameter section of the shank during impact. As a result, localized burning and/or galling of the shank splines in the area between the head of the drill bit and the chuck often results, which can lead to accelerated fatigue failure and then part failure. Accordingly, there is a need for a DHD hammer that is not limited by the aforementioned problems associated with conventional DHD hammers.